probably because of the belief that being gay was a choice and ergo a chosen undesirable to some behaviour you dont choose your ethnicity so you cant really associate that with bad behaviour even though people do because calling someone a nigger or a racerelevant slur more often than not literally just means they are blackof their race many people still believe that being gay is a choice hell i know some of my friends do and i consider it a stupid belief but the stigma is there